The invention relates to a laser amplifying system with a solid-state member having a laser-active medium and with a radiation field system determined by an optical guide means for the radiation field and an actively switchable optical switching element arranged in the radiation field system for influencing the losses in the radiation field system.
Laser amplifying systems of this type are known from the state of the art, wherein during a pass through the radiation field system not only the optical switching element but also the solid-state member having the laser-amplifying medium are normally passed through once.
Since an optical switching element can never be switched free from losses but always has a minimum loss for laser radiation passing through it, this design for laser amplifying systems with a low-amplification laser-active medium is a problem.
The object underlying the invention is therefore to improve a laser amplifying system of the generic type in such a manner that this is suitable for low-amplification laser-active media.
This object is accomplished in accordance with the invention, in a laser amplifying system of the type described at the outset, in that the solid-state member is designed like a thin plate, that the radiation field system comprises an incoming branch and an outgoing branch which are, on the one hand, coupled to one another and between which, on the other hand, an amplifying radiation field is provided which is formed from a plurality of intermediate branches which extend between two optical beam reversing elements and, for their part, all penetrate the solid-state member in a direction transverse to its flat sides and within a volume area, wherein the active volume area has, in directions transverse to beam axes of the intermediate branches, an extension which corresponds at the most to three times the average extension of the radiation field cross sections of the volume sections of the intermediate branches located in the active volume area.
The advantage of the inventive solution is, therefore, to be seen in the fact that due to the provision of the amplifying radiation field with the intermediate branches a high amplification is possible with a multiple pass through the solid-state member designed like a thin plate without the respective losses of the actively switchable optical element having a negative effect on the amplification and without the beam quality suffering.
In addition, the advantage of the inventive solution is also to be seen in the fact that, with it, a large optical path length of the amplifying radiation field can be realized between the respective passes through the switching element and so, as a result, it is possible to use a switching element which operates slowly, for example, in the microsecond range with switching flanks in the range of more than ten nanoseconds.
A solid-state member which is designed like a thin plate is to be understood in accordance with the invention as a solid-state member, the flat sides of which have an extension which is at least ten times, even better one hundred times, the thickness thereof.
Solid-state members which are designed like thin plates and can customarily be used are described, for example, in European patent application No. 0 632 551.
With respect to the arrangement of the actively switchable optical switching element, the most varied of possibilities are conceivable. For example, it would, in principle, be conceivable to arrange the actively switchable optical switching element in one of the intermediate branches of the amplifying radiation field.
It is particularly favorable when the actively switchable optical switching element is arranged outside the amplifying radiation field.
One advantageous solution provides, in this respect, for the actively switchable optical switching element to be arranged in the incoming or outgoing branch of the radiation field system.
In principle, it is sufficient in the inventive solution to provide an amplifying radiation field with a plurality of intermediate branches. If, however, the optical path length of the radiation field system is intended to be maximized, it is also conceivable for the radiation field system to have at least two amplifying radiation fields and for two beam reversing elements to be associated with each amplifying radiation field, wherein both amplifying radiation fields can also extend between the same beam deflecting elements.
With respect to the number of volume areas having a laser-active medium, it is likewise advantageous when providing several amplifying radiation fields when different volume areas having a laser-active medium are associated with the different amplifying radiation fields.
With respect to the construction of the radiation field optical guide means for determining the amplifying radiation field, the most varied of possibilities are conceivable. A particularly favorable solution, in particular, with respect to the transfer properties from intermediate branch to intermediate branch provides for at least one transfer element arranged between the beam reversing elements to be associated with each amplifying radiation field, this transfer element preferably bringing the beam axes of the intermediate branches together in an area of intersection, in which they overlap with their radiation field cross sections at least by half.
It is even better when the intermediate branches overlap with their radiation field cross sections in the area of intersection by at least two thirds, even better overlap for the most part.
The transfer element may, in this respect, be a transfer element operating in transmission. It is, however, particularly favorable when the transfer element is designed to reflect the intermediate branches since such a transfer element allows operations with small losses.
A particularly advantageous variation of a transfer element designed to be reflecting provides for this to be designed as a reflector with a curved reflection surface and, therefore, represent at the same time a folding element for the intermediate branches.
The transfer element may, in principle, have different imaging properties. One particularly advantageous solution provides for the transfer element to be designed as a transfer element acting in a collimating manner for the beam axes of the intermediate branches, i.e., allowing intermediate branches proceeding from an area of intersection to extend parallel to one another following the imaging.
An alternative development likewise preferred within the scope of the inventive solution provides for the transfer element to be designed as a transfer element bringing the beam axes of the intermediate branches together twice in an area of intersection, i.e., the transfer element causes intermediate branches proceeding from an area of intersection to run together again in an area of intersection due to imaging.
The provision of one transfer element acting on the intermediate branches between the beam reversing elements is, in this respect, not a final determination; within the scope of the inventive solution it is also conceivable to provide several transfer elements, depending on the transfer to be carried out.
In the same way, the determination of two beam reversing elements is merely a minimum condition for the determination of the respective amplifying radiation field. It is also conceivable within the scope of the invention to provide additional deflecting elements, for example, multiple deflection elements.
With respect to the beam reversing elements, no further details have been given in conjunction with the preceding explanations concerning the individual embodiments.
The beam reversing elements are preferably designed such that at least some of the intermediate branches extend in the amplifying radiation field, to a great extent, spatially separated.
A favorable variation provides for intermediate branches to extend essentially spatially separate from one another.
Another solution provides for two respective intermediate branches to coincide geometrically but to extend with different directions of radiation propagation.
For example, the beam reversing elements reflect several times, i.e., for example, are designed to reflect twice and convert one intermediate branch into a next intermediate branch extending at a distance from it.
However, a particularly favorable solution provides for at least one of the beam reversing elements to be designed as a single-reflection reflector and, therefore, to convert one intermediate branch as a result of a one-time reflection into the next intermediate branch which can either coincide geometrically with the incoming intermediate branch or extend at an angle to it.
The advantage of this solution is, on the one hand, that the losses during the reflection can be minimized. On the other hand, the advantage is also that, as a result, one intermediate branch can, in a simple manner, be converted into an intermediate branch coinciding with it geometrically but propagating in the opposite direction in a simple manner.
In this respect, it is particularly advantageous when both beam reversing elements are designed as single-reflection reflectors.
In the case where the beam reversing element is designed as a single-reflection reflector, it is particularly advantageous when the intermediate branches impinge on the reflector in a surface area with their radiation field cross sections overlapping so that they are reflected back from this surface area which represents an area of intersection.
With respect to the course of the intermediate branches in the active volume area, no further specific details have been given in conjunction with the preceding embodiments. It is particularly favorable when the intermediate branches essentially overlap with their volume sections penetrating the active volume area in order to achieve as effective a coupling as possible to the same excited volume area in the solid-state member as a result.
This coupling may be brought about in a particularly favorable manner when the optical guide means for the radiation field is designed in such a manner that the intermediate branches each have an approximately similar radiation field geometry in the active volume area and, therefore, are coupled to the laser-active volume area in as efficient a form as possible.
In order to achieve transfer ratios in the radiation field system which are as good as possible, the optical guide means for the radiation field is preferably designed in such a manner that the beam axes of the intermediate branches penetrate a volume of intersection which is located in a spatial area comprising the active volume area, is smaller than the active volume area by at least a factor of 10, even better a factor of 100, and the extension of which in the individual spatial directions is preferably smaller than the extension of the active volume area in the individual spatial directions by a factor of 10, even better 100.
This means that the volume of intersection is intended to be located either in the active volume area or close to it.
In order to limit the spatial area, in which the volume of intersection is preferably located, it is preferably provided for the spatial area to have in every direction a maximum extension which corresponds to double the maximum extension of the active volume area so that the active volume area is always located close to the volume of intersection.
A particularly favorable solution provides for the solid-state member having the laser-active medium to be arranged directly in front of the beam reversing element, on which the intermediate branches overlap in the surface area with their radiation cross sections.
In order to obtain conditions which are as optimum as possible, it is preferably provided for the optical guide means for the radiation field to be designed in such a manner that the intermediate branches with approximately the same beam propagation direction have an identical symmetry with an identical alignment of symmetry within the active volume area.
This means that the amplifying radiation field is designed in this case such that each intermediate branch has the same symmetry within the active volume area and is also aligned such that the directions of symmetry essentially coincide.
Furthermore, an advantageous solution provides for the optical guide means for the radiation field to be designed in such a manner that the intermediate branches with approximately the same beam propagation direction have approximately the same phase curvature in the active volume area so that phase distortions from intermediate branch to intermediate branch are avoided.
In this respect, it is particularly favorable when the optical guide means for the radiation field is designed in such a manner that the intermediate branches with approximately the same beam propagation direction have conjugated surfaces located in a spatial area comprising the active volume area.
In this respect, the spatial area is preferably defined in such a manner that this has in every direction a maximum extension which corresponds to double the maximum extension of the active volume area in this direction.
Particularly favorable imaging conditions result, in addition, when the optical guide means for the radiation field is designed in such a manner that the amplifying radiation field behaves like an afocal system within the active volume. In order to achieve distortions in the radiation field which are as slight as possible, it is preferably provided for the optical guide means for the radiation field to be designed in such a manner that a different intermediate branch with an imaging magnification of approximately one is formed from each of the intermediate branches.
Since, in the case of the inventive solution, the number of intermediate branches determines the optical path length in the amplifying radiation field and pulse duration and repetitive frequency influence this optical path length in pulsed operation for the propagating times, it is preferably provided for the number of intermediate branches to be adjustable due to adjustment relative to one another of the elements of the optical guide means for the radiation field defining the amplifying radiation field.
This may be realized particularly favorably when the number of intermediate branches can be adjusted due to adjustment of one of the beam reversing elements relative to the other, stationarily arranged elements of the optical guide means for the radiation field.
No further details have so far been given with respect to the path of the incoming branch relative to the elements of the optical guide means for the radiation field. One advantageous embodiment provides, for example, for the incoming branch to extend between an end element of the optical guide means for the radiation field and one of the two beam reversing elements.
Also with respect to the arrangement of the outgoing branch, no further details have so far been given. It is expedient when the outgoing branch extends between an end element of the optical guide means for the radiation field and one of the beam reversing elements.
A particularly expedient solution provides for the incoming branch and the outgoing branch to extend towards the same beam reversing element.
No further details have so far been given with respect to the coupling between the incoming branch and the outgoing branch. The coupling can be realized, for example, in the most varied of ways.
One advantageous possibility provides for the incoming branch and the outgoing branch to be coupled directly by means of the end elements, i.e., the end elements are arranged such that they transfer the incoming and the outgoing branches directly into one another.
For example, this is possible due to the fact that the end elements couple the outgoing branch and the incoming branch by way of reflection.
This is possible, on the one hand, due to the fact that the incoming branch and the outgoing branch extend at a distance to one another and are coupled by means of reflecting end elements arranged in a suitable manner.
Another possibility provides for the incoming branch and the outgoing branch to extend towards the same end element and to be arranged such that they coincide geometrically so that the incoming branch results again due to reflection back of the outgoing branch.
No further details have so far been given with respect to the design of the radiation field system and the propagation of the laser radiation in the radiation field system.
One advantageous embodiment, for example, provides for laser radiation to be able to pass through the radiation field system several times in the same direction of pass.
An alternative solution to this provides for the radiation field system to be designed such that laser radiation can pass through the radiation field system in opposite directions due to a reversal of direction in the incoming and/or outgoing branch.
No further details have so far been given with respect to the coupling of the laser radiation out of the radiation field system. One advantageous embodiment, for example, provides for part of the laser radiation to be constantly coupled out in the radiation field system, i.e., for the laser radiation coupled out to always correspond to an approximately constant proportion of the laser radiation in the radiation field system.
This may be achieved, for example, due to the fact that the laser radiation can be coupled out by an element of the optical guide means for the radiation field which is designed, for example, as a partially transparent mirror.
Another advantageous solution provides for laser radiation to pass through the radiation field system for such a time until an active coupling out is brought about by means of the optical switching element.
In this case, the optical switching element serves not only to influence the losses in the radiation field system but, at the same time, to couple laser radiation out of the radiation field system in an actively controlled manner.
For this purpose, the actively switchable optical switching element may be designed in the most varied of ways.
One advantageous possibility provides, for example, for the actively switchable optical switching element to be a switching element influencing polarization.
In this case, the switching element influencing polarization preferably carries out a change in the polarization which then causes a complete or partial, actively controlled coupling of laser radiation out of the radiation field system in combination with a reflector dependent on polarization.
Another advantageous solution provides for the actively switchable optical switching element to be a switching element diffracting radiation, i.e., the laser radiation is coupled out of the radiation field system by way of diffraction.
For example, the actively switchable optical switching element is designed in this respect as an acousto-optical modulator which acts in a manner diffracting radiation by means of a sound wave field.
The solid-state member designed like a thin plate can, furthermore, be advantageously defined by the fact that this has a thickness which corresponds at the most to a tenth, even better one hundredth of its smallest extension in the direction of a flat side.
With respect to the arrangement of the solid-state member itself, no further details have been given in conjunction with the preceding explanations concerning the inventive solution. One particularly favorable solution, for example, provides for the solid-state member to be cooled via a flat side by means of a heat sink in order to prevent thermal tensions and a thermal formation of lenses in it.
For example, the heat sink is a cooling medium or a cooling member. In this respect, the solid-state member is preferably arranged on a cooling member and supported by it.
The laser-active medium in the solid-state member is preferably a laser-active material with a low amplification, as described, for example, in European patent No. 0 632 551.
Furthermore, the solid-state member preferably has a laser-active material with a high saturation intensity, as described, for example, in European patent No. 0 632 551.